Relaying units switching between energizing and de-energizing a load (also called “relay units”) may be provided with mechanical switching elements containing normally open contacts (a contacts) and normally closed contacts (b contacts). Refer to European Patent Application Publication No.: EP1202313A1 (Published 2 May 2002) and Patent Document 2: Japanese Utility Model Application Publication No. H05-55435 (Published 23 Jul. 1993), for example.